domingo, 24 de marzo de 2013

The Largest Structure in Observable Universe --Quasar Group 4 Billion Light-Years Wide

On the 50th Anniversary of the discovery of the quasar, we thanought
it timely to do a weekend feature on the recent discovery oftThe largest
known structure in the universe . The large quasar group (LQG -a
portion shown above)) is so large that it would take a spaceship
traveling at the speed of light some 4 billion years to cross it.

Quasars are the nuclei of galaxies from the early days of the universe
that undergo brief periods of extremely high brightness that make them
visible across huge distances. These periods are 'brief' in astrophysics
terms but actually last 10-100 million years. Since 1982 it has been
known that quasars tend to group together in clumps or 'structures' of surprisingly large sizes, forming large quasar groups or LQGs.

The LQG also challenges the Cosmological Principle,
the assumption that the universe, when viewed at a sufficiently large
scale, looks the same no matter where you are observing it from. The
modern theory of cosmology is based on the work of Albert Einstein,
and depends on the assumption of the Cosmological Principle. The
Principle is assumed but has never been demonstrated observationally
'beyond reasonable doubt'.

Whole clusters of galaxies can be 2-3 Mpc across but LQGs can be 200
Mpc or more across. Based on the Cosmological Principle and the modern
theory of cosmology, calculations suggest that astrophysicists should
not be able to find a structure larger than 370 Mpc. Clowes' newly
discovered LQG however has a typical dimension of 500 Mpc. But because
it is elongated, its longest dimension is 1200 Mpc (or 4 billion light
years) - some 1600 times larger than the distance from the Milky Way to
Andromeda.

"While it is difficult to fathom the scale of this LQG, we can say
quite definitely it is the largest structure ever seen in the entire
universe," said Dr Clowes of University of Central Lancashire'sJeremiah Horrocks Institute.

"This is hugely exciting – not least because it runs counter to our
current understanding of the scale of the universe. Even travelling at
the speed of light, it would take 4 billion years to cross. This is
significant not just because of its size but also because it challenges
the Cosmological Principle, which has been widely accepted since
Einstein. Our team has been looking at similar cases which add further
weight to this challenge and we will be continuing to investigate these
fascinating phenomena."

The colored background of the image below indicates the peaks and
troughs in the occurrence of quasars at the distance of the LQG. Darker
colors indicate more quasars, lighter colors indicate fewer quasars. The
LQG is clearly seen as a long chain of peaks indicated by black
circles. (The red crosses mark the positions of quasars in a different
and smaller LQG). The horizontal and vertical axes represent right
ascension and declination, the celestial equivalent of longitude and
latitude. The map covers around 29.4 by 24 degrees on the sky,
indicating the huge scale of the newly discovered structure.